--- /dev/null
+// Copyright (c) 2014 Marshall A. Greenblatt. Portions copyright (c) 2012
+// Google Inc. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google Inc. nor the name Chromium Embedded
+// Framework nor the names of its contributors may be used to endorse
+// or promote products derived from this software without specific prior
+// written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef CEF_INCLUDE_BASE_CEF_MOVE_H_
+#define CEF_INCLUDE_BASE_CEF_MOVE_H_
+
+#if defined(MOVE_ONLY_TYPE_FOR_CPP_03)
+// Do nothing if the macro in this header has already been defined.
+// This can happen in cases where Chromium code is used directly by the
+// client application. When using Chromium code directly always include
+// the Chromium header first to avoid type conflicts.
+#elif defined(USING_CHROMIUM_INCLUDES)
+// When building CEF include the Chromium header directly.
+#include "base/move.h"
+#else // !USING_CHROMIUM_INCLUDES
+// The following is substantially similar to the Chromium implementation.
+// If the Chromium implementation diverges the below implementation should be
+// updated to match.
+
+// Macro with the boilerplate that makes a type move-only in C++03.
+//
+// USAGE
+//
+// This macro should be used instead of DISALLOW_COPY_AND_ASSIGN to create
+// a "move-only" type. Unlike DISALLOW_COPY_AND_ASSIGN, this macro should be
+// the first line in a class declaration.
+//
+// A class using this macro must call .Pass() (or somehow be an r-value already)
+// before it can be:
+//
+// * Passed as a function argument
+// * Used as the right-hand side of an assignment
+// * Returned from a function
+//
+// Each class will still need to define their own "move constructor" and "move
+// operator=" to make this useful. Here's an example of the macro, the move
+// constructor, and the move operator= from the scoped_ptr class:
+//
+// template <typename T>
+// class scoped_ptr {
+// MOVE_ONLY_TYPE_FOR_CPP_03(scoped_ptr, RValue)
+// public:
+// scoped_ptr(RValue& other) : ptr_(other.release()) { }
+// scoped_ptr& operator=(RValue& other) {
+// swap(other);
+// return *this;
+// }
+// };
+//
+// Note that the constructor must NOT be marked explicit.
+//
+// For consistency, the second parameter to the macro should always be RValue
+// unless you have a strong reason to do otherwise. It is only exposed as a
+// macro parameter so that the move constructor and move operator= don't look
+// like they're using a phantom type.
+//
+//
+// HOW THIS WORKS
+//
+// For a thorough explanation of this technique, see:
+//
+// http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Move_Constructor
+//
+// The summary is that we take advantage of 2 properties:
+//
+// 1) non-const references will not bind to r-values.
+// 2) C++ can apply one user-defined conversion when initializing a
+// variable.
+//
+// The first lets us disable the copy constructor and assignment operator
+// by declaring private version of them with a non-const reference parameter.
+//
+// For l-values, direct initialization still fails like in
+// DISALLOW_COPY_AND_ASSIGN because the copy constructor and assignment
+// operators are private.
+//
+// For r-values, the situation is different. The copy constructor and
+// assignment operator are not viable due to (1), so we are trying to call
+// a non-existent constructor and non-existing operator= rather than a private
+// one. Since we have not committed an error quite yet, we can provide an
+// alternate conversion sequence and a constructor. We add
+//
+// * a private struct named "RValue"
+// * a user-defined conversion "operator RValue()"
+// * a "move constructor" and "move operator=" that take the RValue& as
+// their sole parameter.
+//
+// Only r-values will trigger this sequence and execute our "move constructor"
+// or "move operator=." L-values will match the private copy constructor and
+// operator= first giving a "private in this context" error. This combination
+// gives us a move-only type.
+//
+// For signaling a destructive transfer of data from an l-value, we provide a
+// method named Pass() which creates an r-value for the current instance
+// triggering the move constructor or move operator=.
+//
+// Other ways to get r-values is to use the result of an expression like a
+// function call.
+//
+// Here's an example with comments explaining what gets triggered where:
+//
+// class Foo {
+// MOVE_ONLY_TYPE_FOR_CPP_03(Foo, RValue);
+//
+// public:
+// ... API ...
+// Foo(RValue other); // Move constructor.
+// Foo& operator=(RValue rhs); // Move operator=
+// };
+//
+// Foo MakeFoo(); // Function that returns a Foo.
+//
+// Foo f;
+// Foo f_copy(f); // ERROR: Foo(Foo&) is private in this context.
+// Foo f_assign;
+// f_assign = f; // ERROR: operator=(Foo&) is private in this context.
+//
+//
+// Foo f(MakeFoo()); // R-value so alternate conversion executed.
+// Foo f_copy(f.Pass()); // R-value so alternate conversion executed.
+// f = f_copy.Pass(); // R-value so alternate conversion executed.
+//
+//
+// IMPLEMENTATION SUBTLETIES WITH RValue
+//
+// The RValue struct is just a container for a pointer back to the original
+// object. It should only ever be created as a temporary, and no external
+// class should ever declare it or use it in a parameter.
+//
+// It is tempting to want to use the RValue type in function parameters, but
+// excluding the limited usage here for the move constructor and move
+// operator=, doing so would mean that the function could take both r-values
+// and l-values equially which is unexpected. See COMPARED To Boost.Move for
+// more details.
+//
+// An alternate, and incorrect, implementation of the RValue class used by
+// Boost.Move makes RValue a fieldless child of the move-only type. RValue&
+// is then used in place of RValue in the various operators. The RValue& is
+// "created" by doing *reinterpret_cast<RValue*>(this). This has the appeal
+// of never creating a temporary RValue struct even with optimizations
+// disabled. Also, by virtue of inheritance you can treat the RValue
+// reference as if it were the move-only type itself. Unfortunately,
+// using the result of this reinterpret_cast<> is actually undefined behavior
+// due to C++98 5.2.10.7. In certain compilers (e.g., NaCl) the optimizer
+// will generate non-working code.
+//
+// In optimized builds, both implementations generate the same assembly so we
+// choose the one that adheres to the standard.
+//
+//
+// WHY HAVE typedef void MoveOnlyTypeForCPP03
+//
+// Callback<>/Bind() needs to understand movable-but-not-copyable semantics
+// to call .Pass() appropriately when it is expected to transfer the value.
+// The cryptic typedef MoveOnlyTypeForCPP03 is added to make this check
+// easy and automatic in helper templates for Callback<>/Bind().
+// See IsMoveOnlyType template and its usage in base/callback_internal.h
+// for more details.
+//
+//
+// COMPARED TO C++11
+//
+// In C++11, you would implement this functionality using an r-value reference
+// and our .Pass() method would be replaced with a call to std::move().
+//
+// This emulation also has a deficiency where it uses up the single
+// user-defined conversion allowed by C++ during initialization. This can
+// cause problems in some API edge cases. For instance, in scoped_ptr, it is
+// impossible to make a function "void Foo(scoped_ptr<Parent> p)" accept a
+// value of type scoped_ptr<Child> even if you add a constructor to
+// scoped_ptr<> that would make it look like it should work. C++11 does not
+// have this deficiency.
+//
+//
+// COMPARED TO Boost.Move
+//
+// Our implementation similar to Boost.Move, but we keep the RValue struct
+// private to the move-only type, and we don't use the reinterpret_cast<> hack.
+//
+// In Boost.Move, RValue is the boost::rv<> template. This type can be used
+// when writing APIs like:
+//
+// void MyFunc(boost::rv<Foo>& f)
+//
+// that can take advantage of rv<> to avoid extra copies of a type. However you
+// would still be able to call this version of MyFunc with an l-value:
+//
+// Foo f;
+// MyFunc(f); // Uh oh, we probably just destroyed |f| w/o calling Pass().
+//
+// unless someone is very careful to also declare a parallel override like:
+//
+// void MyFunc(const Foo& f)
+//
+// that would catch the l-values first. This was declared unsafe in C++11 and
+// a C++11 compiler will explicitly fail MyFunc(f). Unfortunately, we cannot
+// ensure this in C++03.
+//
+// Since we have no need for writing such APIs yet, our implementation keeps
+// RValue private and uses a .Pass() method to do the conversion instead of
+// trying to write a version of "std::move()." Writing an API like std::move()
+// would require the RValue struct to be public.
+//
+//
+// CAVEATS
+//
+// If you include a move-only type as a field inside a class that does not
+// explicitly declare a copy constructor, the containing class's implicit
+// copy constructor will change from Containing(const Containing&) to
+// Containing(Containing&). This can cause some unexpected errors.
+//
+// http://llvm.org/bugs/show_bug.cgi?id=11528
+//
+// The workaround is to explicitly declare your copy constructor.
+//
+#define MOVE_ONLY_TYPE_FOR_CPP_03(type, rvalue_type) \
+ private: \
+ struct rvalue_type { \
+ explicit rvalue_type(type* object) : object(object) {} \
+ type* object; \
+ }; \
+ type(type&); \
+ void operator=(type&); \
+ public: \
+ operator rvalue_type() { return rvalue_type(this); } \
+ type Pass() { return type(rvalue_type(this)); } \
+ typedef void MoveOnlyTypeForCPP03; \
+ private:
+
+#endif // !USING_CHROMIUM_INCLUDES
+
+#endif // CEF_INCLUDE_BASE_CEF_MOVE_H_
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